The present invention relates to a new and distinctive corn inbred line, designated GSC2. There are numerous steps in the development of any novel, desirable plant germplasm. The first step is to define and analyze the problems and weaknesses of the current germplasm, establish the program goals, and define the specific breeding objectives. The next step is to select germplasm that possess the traits that meet the program goals. The ultimate goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These traits may include higher yield, better resistance to diseases and insects, better stalks and roots, increased tolerance to drought and heat, and better agronomic quality.
Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F.sub.1 hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a few locations is effective, whereas, for low heritable traits, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods include pedigree selection, modified pedigree selection, mass selection, and recurrent selection.
The complexity of inheritance influences the choice of breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination and the number of hybrid offspring from each successful cross.
Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, however, each evaluation should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.).
Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) a minimum of three years. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection.
This process, which leads to the final step of marketing and distribution, usually take from eight to twelve years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and minimum changes in direction.
The true genotypic value of most traits is masked by other confounding plant traits and/or environmental factors making it difficult to identify genetically superior individuals. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations are made to provide a better estimate of the plant's genetic worth.
The goal of plant breeding is to develop new, unique and superior corn inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutating. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same corn traits.
Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The resulting inbred lines are unpredictable. This unpredictability occurs because the breeder's selection is made in unique environments, with no control at the DNA level (using conventional breeding procedures), and different genetic combinations being generated. A breeder of ordinary skill cannot predict the resulting lines except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice even using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new corn inbred line.
The development of commercial corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines; the hybrids from these crosses are evaluated to determine which have commercial potential.
Pedigree breeding is used commonly to improve self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F.sub.1 : An F.sub.2 population is produced by selfing one or several F.sub.1 's or by intercrossing two F.sub.1 's (sib mating). Selection of the best individuals usually begins in the F.sub.2 population; then, in the F.sub.3 line, the best individuals in the best families are selected. Replicated tests of families, or hybrid combinations of individuals within these families, often follow in the F.sub.4 generation to improve the effectiveness of the selection of low heritable traits. In the advanced stages of inbreeding (i.e., F.sub.6 and F.sub.7), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars.
Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued.
Backcross breeding can be used to transfer genes of a highly heritable trait into a desirable homozygous cultivar or inbred line (the recurrent parent). The source of the transferred trait is called the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent.
Descriptions of other breeding methods commonly used for different: traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987).
Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is comparable with industry standards or that creates a new market. The seed producer, grower, processor, and consumer will incur additional costs with the introduction of a new cultivar for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding the release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, easy and economical seed production must be feasible.
Once the best-performing inbreds have been identified, the hybrid seed can be reproduced indefinitely provided the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced by crossing two inbred lines to produce the F.sub.1 progeny (A.times.B). A double-cross hybrid is produced by crossing two desirable single crosses (A.times.B).times.(C.times.D). Much of the hybrid vigor exhibited by F.sub.1 hybrids is lost in the next generation (F.sub.2). Consequently, seed from hybrid varieties is not used for planting stock.
Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding, agronomically sound corn hybrids. The reasons for this goal are to maximize the amount of grain produced and to supply food for both animals and humans. To accomplish this goal, the corn breeder must select and develop corn plants that have the traits that result in superior parental lines for producing hybrids.